It has been established by the researchers that owing to the arching effect, the active earth pressure distribution on a horizontally translating rigid wall is not triangular but nonlinear. This is ...attributed to the arching behavior exhibited by soil. Also, the shape of the failure surface plays a critical role in determining the magnitude of lateral stresses and the height at which the resultant active earth force is centered from the base of the wall. In the present study, various combinations of shapes of critical failure surface and arch shapes were studied to estimate the coefficient of active earth pressure on the rigid retaining wall in cohesionless soil. The results were compared with field results and those predicted by other theories. A critical review has been made based on the comparison of results obtained from the present analyses with experimental observations. Design charts for modified active earth pressure coefficient and height of application of lateral force have also been suggested.
AbstractSoil stress-strain behavior is highly nonlinear and considerably influences the performance of a foundation. The response of single piles under axial load can be predicted from the ...load-transfer, or t-z, curve. This paper presents a new approach to predict the load-transfer curve and subsequently the load-settlement curve. This new approach incorporates nonlinear soil stress-strain behavior and accommodates differences in soil behavior in laboratory and field conditions. Expressions are given for the load-transfer curve, which capture the hardening and softening behavior of soil-pile interactions. Predictions of load-transfer curves and load-settlement curves from the proposed approach have been compared with the measured values from two case studies. The predictions show good agreement with the measured values.
ABSTRACT
Aiming to fill a crucial gap in our observational knowledge of the early Universe, experiments around the world continue to attempt to verify the claimed detection of the redshifted 21-cm ...signal from Cosmic Dawn by the EDGES experiment. This sky-averaged or ‘global’ signal from neutral hydrogen should be detectable at low radio frequencies (50–200 MHz), but is difficult to measure due to bright foreground emission and difficulties in reaching the required levels of instrumental-calibration precision. In this paper, we outline our progress toward using a novel new method to measure the global redshifted 21-cm signal. Motivated by the need to use alternative methods with very different systematic errors to EDGES for an independent result, we employ an array of closely spaced antennas to measure the global-sky signal interferometrically, rather than using the conventional approach with a single antenna. We use simulations to demonstrate our newly developed methods and show that, for an idealized instrument, a 21-cm signal could theoretically be extracted from the visibilities of an array of closely spaced dipoles. We verify that our signal-extraction methods work on real data using observations made with a Square-Kilometre-Array-like prototype, the Engineering Development Array-2. Finally, we use the lessons learned in both our simulations and observations to lay out a clear plan for future work, which will ultimately lead to a new global redshifted 21-cm instrument: the All-Sky SignAl Short-Spacing INterferometer (ASSASSIN).
This paper presents the dynamic response analysis of Talcher pond ash embankment in India, considering both full saturation and existing water table condition subjected to earthquake excitation. ...Static and cyclic triaxial tests were performed to determine the parameters required for the dynamic response analysis of the existing pond ash embankment. From the cyclic triaxial test, it is observed that Talcher pond ash is susceptible to liquefaction. A two dimensional nonlinear finite element analysis using Open System for earthquake engineering simulation (OpenSees) has been carried out to study the dynamic response analysis of the existing embankment. The pre and postprocessing phases have been done using GiD 7.2 software. The North East India earthquake, May 08, 1997 (Motion 1) and North East India earthquake, Aug 06, 1988 (Motion 2) have been used as the input motion for the dynamic response analysis. The model has been validated with the results of cyclic triaxial test performed on Talcher pond ash. From analysis, it is observed that under full saturation condition, the maximum horizontal and vertical displacement below the slope of the embankment is 4.505m and 3.247m respectively. Also the pore pressure ratio below the slope is observed more than unity. The pond ash embankment is not safe against liquefaction and lateral spreading under full saturation condition. However, under existing water table condition the embankment is safe against liquefaction.
We present Giant Metrewave Radio Telescope H i observations and deep Canada–France–Hawaii Telescope (CFHT) MegaCam optical images of the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 ...(hereafter NGC 871/6/7). Our high-resolution data sets provide a census of the H i and stellar properties of the detected gas-rich group members. In addition to a handful of spiral, irregular and dwarf galaxies, this group harbours an intriguing H i feature, AGC 749170, that has a gas mass of ∼109.3 M⊙, a dynamical-to-gas mass ratio of ∼1 (assuming that the cloud is rotating and in dynamical equilibrium) and no optical counterpart in previous imaging. Our observations have revealed a faint feature in the CFHT g
′ and r
′ bands; if it is physically associated with AGC 749170, the latter has
$M/L_{\rm g} >1000 \,\mathrm{M}_{{\odot }}/\mathrm{L}_{{\odot }}$
as well as a higher metallicity (estimated using photometric colours) and a significantly younger stellar population than the other low-mass gas-rich group members. These properties, as well as its spectral and spatial location with respect to its suspected parent galaxies, strongly indicate a tidal origin for AGC 749170. Overall, the H i properties of AGC 749170 resemble those of other optically dark/dim clouds that have been found in groups. These clouds could represent a class of relatively long-lived H i-rich tidal remnants that survive in intermediate-density environments.
We present high-resolution Giant Metrewave Radio Telescope (GMRT) H i observations and deep Canada–France–Hawaii Telescope (CFHT) optical imaging of two galaxy groups: NGC 4725/47 and NGC 3166/9. ...These data are part of a multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal knots and one dwarf irregular galaxy (dIrr). Both tidal knots are located within a prominent H i tidal tail, appear to have sufficient mass (M
gas ≈ 108 M⊙) to evolve into long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC 3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and four H i knots. Deep CFHT imaging confirms that the optical component of AGC 208457 is bluer – with a 0.28 mag g − r colour – and a few Gyr younger than its purported parent galaxies. Combining the results for these groups with those from the NGC 871/6/7 group reported earlier, we find that the H i properties, estimated stellar ages and baryonic content of the gas-rich dwarfs clearly distinguish tidal features from their classical counterparts. We optimistically identify four potentially long-lived tidal objects associated with three separate pairs of interacting galaxies, implying that TDGs are not readily produced during interaction events as suggested by some recent simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than TDGs of similar mass formed in current simulations of interacting galaxies, which could be the result of pre- or post-formation environmental influences.
We study the conditions under which carbon clusters of different sizes form and stabilize. We describe the approach to equilibrium by simulating tenuous carbon gas dynamics to long times. First, we ...use reactive molecular dynamics simulations to describe the nucleation of long chains, large clusters, and complex cage structures in carbon- and hydrogen-rich interstellar gas phases. We study how temperature, particle density, the presence of hydrogen, and carbon inflow affect the nucleation of molecular moieties with different characteristics, in accordance with astrophysical conditions. We extend the simulations to densities that are orders of magnitude lower than current laboratory densities, to temperatures that are relevant to circumstellar environments of planetary nebulae, and microsecond formation times. We correlate cluster size distributions from the simulations with thermodynamic equilibrium at low temperatures and gas densities, where entropy plays a significant role.
The expanded Giant Metrewave Radio Telescope Patra, N N; Kanekar, N; Chengalur, J N ...
Monthly notices of the Royal Astronomical Society,
03/2019, Letnik:
483, Številka:
3
Journal Article
PDF
